1. Field of the Invention
This invention relates to a swivel adapted for transferring fluids. In particular, it relates to a product swivel adapted for assuring the passage of a pig through the swivel.
2. Description of the Prior Art
The offshore search for oil and gas has greatly expanded in recent years and progressed into deep, rough waters such as the North Sea. To facilitate production of oil and gas from remotely located offshore fields, complex tanker mooring systems which serve as centralized production sites for the entire field have been developed. Flexible fuel lines extend from a subsea location to the mooring site to permit the transfer of fluids between a moored tanker and a subsea location. For example, certain fluids lines may be used to convey oil and gas into the tanker, while other fluid lines may be used to inject liquids or gases back into the field for the purpose of well stimulation or storage.
Tankers will usually be moored to a single point mooring system which permits the vessel to weather vane and rotate 360 degrees about a single mooring point. To permit the tanker to rotate and move freely without causing twisting or entanglement of the various fluid lines to which the tanker is attached, it is necessary to provide a swivel mechanism to connect the fluid lines to the mooring site. Furthermore, since a plurality of fluid lines are involved, it is necessary that such a swivel have the capability of accommodating multiple lines.
The state of the art of product swivels and multi-line product swivels is illustrated in my co-pending patent application Ser. No. 635,922, "High Pressure Product Swivel" filed July 30, 1984 and is incorporated by reference into this application for all purposes. I am the sole inventor of both this application and the above referenced co-pending patent application.
The conveyance of oil, gas, and other well fluids often results in the formation of paraffin deposits and the accumulation of corrosion on the pipeline walls and the conduit chamber of the swivel. These accumulations and deposits reduce the efficiency of the conveyance system by increasing the impedance to fluid flow. In order to clean the pipeline walls and chamber of the swivel, a conventional ball or plug shaped scraper pig is passed under pressure through the conveyance system.
Also, in addition to a scraper pig, a separator pig may be used for separating different batches of product through a conveyance system incorporating the product swivel. It is to be understood that hereinafter a pig refers to either a scraper pig or a separator pig.
In prior art swivels, a pig passing through the conduit chamber of the swivel could become misrouted at a junction adjacent an inlet or an outlet of the swivel and could inadvertently become lodged in the junction. The pressurized fluid forcing the pig through the swivel could then by-pass the pig thereby preventing its proper passage from the inlet to the outlet of the swivel or, worse, the pig could severly restrict the flow of fluids in the conveyance system.